Systemic Lupus Erythematosus and DNA Degradation and Elimination Defects

Genome-wide characterization of extrachromosomal circular DNA in SLE and functional analysis reveal their association with apoptosis

Extrachromosomal circular DNA (eccDNA) derived from linear chromosomes, are showed typical nucleosomal ladder pattern in agarose gel which as a known feature of apoptosis and demonstrated to be immunogenicity. In systemic lupus erythematosus (SLE) patients, elevated levels of cell-free DNA (cfDNA) can be found in either linear forms or circular forms, while circular ones are much less common and harder to detect. The molecular characteristics and function of circular forms in plasma SLE patients remains elusive. Herein, we characterized the hallmarks of plasma eccDNA in SLE patients, including the lower normalized number and GC content of eccDNA in SLE plasma than in the healthy, and SLE eccDNA number positively correlated with C3 and negatively with anti-dsDNA antibodies. The differential eccGenes (eccDNAs carrying the protein coding gene sequence) of SLE was significantly enriched in apoptosis-related pathways. The artificially synthesized eccDNA with sequences of the PRF1 exon region could promote transcriptional expression of PRF1, IFNA and IFIT3 and inhibit early-stage apoptosis. Plasma eccDNA can serve as a novel autoantigen in the pathogenesis of SLE.

Female-bias in systemic lupus erythematosus: How much is the X chromosome to blame?

Systemic lupus erythematosus (SLE or lupus) is an immune-mediated disease associated with substantial medical burden. Notably, lupus exhibits a striking female bias, with women having significantly higher susceptibility compared to men, up to 14-fold higher in some ethnicities. Supernumerary X chromosome syndromes, like Klinefelter (XXY) and Triple X syndrome (XXX), also present higher SLE prevalence, whereas Turner syndrome (XO) displays lower prevalence. Taken together, SLE prevalence in different X chromosome dosage sceneries denotes a relationship between the number of X chromosomes and the risk of developing lupus. The dosage of X-linked genes, many of which play roles in the immune system, is compensated between males and females through the inactivation of one of the two X chromosomes in female cells. X-chromosome inactivation (XCI) initiates early in development with a random selection of which X chromosome to inactivate, a choice that is then epigenetically maintained in the daughter cells. This process is regulated by the X-Inactive-Specific Transcript (XIST), encoding for a long non-coding RNA, exclusively expressed from the inactive X chromosome (Xi). XIST interacts with various RNA binding proteins and chromatin modifiers to form a ribonucleoprotein (RNP) complex responsible for the transcriptional silencing and heterochromatinization of the Xi. This ensures stable silencing of most genes on the X chromosome, with only a few genes able to escape this process. Recent findings suggest that the molecular components involved in XCI, or their dysregulation, contribute to the pathogenesis of lupus. Indeed, nonrandom XCI, elevated gene escape from XCI, and the autoimmune potential of the XIST RNP complex have been suggested to contribute to auto-immune diseases, such as lupus. This review examines these current hypotheses concerning how this dosage compensation mechanism might impact the development of lupus, shedding light on potential mechanisms underlying the pathogenesis of the disease.

Low-dose IL-2 therapy in autoimmune diseases: An update review

Regulatory T (Treg) cells are essential for maintaining self-immune tolerance. Reduced numbers or functions of Treg cells have been involved in the pathogenesis of various autoimmune diseases and allograft rejection. Therefore, the approaches that increase the pool or suppressive function of Treg cells in vivo could be a general strategy to treat different autoimmune diseases and allograft rejection. Interleukin-2 (IL-2) is essential for the development, survival, maintenance, and function of Treg cells, constitutively expressing the high-affinity receptor of IL-2 and sensitive response to IL-2 in vivo. And low-dose IL-2 therapy in vivo could restore the imbalance between autoimmune response and self-tolerance toward self-tolerance via promoting Treg cell expansion and inhibiting follicular helper T (Tfh) and IL-17-producing helper T (Th17) cell differentiation. Currently, low-dose IL-2 treatment is receiving extensive attention in autoimmune disease and transplantation treatment. In this review, we summarize the biology of IL-2/IL-2 receptor, the mechanisms of low-dose IL-2 therapy in autoimmune diseases, the application in the progress of different autoimmune diseases, including Systemic Lupus Erythematosus (SLE), Type 1 Diabetes (T1D), Rheumatoid Arthritis (RA), Autoimmune Hepatitis (AIH), Alopecia Areata (AA), Immune Thrombocytopenia (ITP) and Chronic graft-versus-host-disease (GVHD). We also discuss the future directions to optimize low-dose IL-2 treatments.

Ex Vivo-Generated Tolerogenic Dendritic Cells: Hope for a Definitive Therapy of Autoimmune Diseases

Current therapies for autoimmune diseases are immunosuppressant agents, which have many debilitating side effects. However, dendritic cells (DCs) can induce antigen-specific tolerance. Tolerance restoration mediated by ex vivo-generated DCs can be a therapeutic approach. Therefore, in this review, we summarize the conceptual framework for developing ex vivo-generated DC strategies for autoimmune diseases. First, we will discuss the role of DCs in developing immune tolerance as a foundation for developing dendritic cell-based immunotherapy for autoimmune diseases. Then, we also discuss relevant findings from pre-clinical and clinical studies of ex vivo-generated DCs for therapy of autoimmune diseases. Finally, we discuss problems and challenges in dendritic cell therapy in autoimmune diseases. Throughout the article, we discuss autoimmune diseases, emphasizing SLE.

The acid sphingomyelinase inhibitor imipramine enhances the release of UV photoproduct-containing DNA in small extracellular vesicles in UVB-irradiated human skin

Nucleic acids, lipids, and other cell components can be found within different types of extracellular vesicles (EVs), which include apoptotic bodies (ABs), large extracellular vesicles (LEVs), and small extracellular vesicles (SEVs). Release of LEVs from cells can be reduced by genetic or pharmacological inhibition of the enzyme acid sphinogomyelinase (aSMase), and indeed several studies have demonstrated a role for the clinically approved aSMase inhibitor imipramine in blocking LEV release, including in response to UVB exposure. Given that exposure of keratinocytes to UVB radiation results in the generation of UVR photoproducts in DNA that can subsequently be found in association with ABs and SEVs, we examined how imipramine impacts the release of extracellular DNA containing UVR photoproducts at an early time point after UVR exposure. Using several different model systems, including cultured keratinocytes in vitro, discarded human surgical skin ex vivo, and skin biopsies obtained from treated human subjects, these pilot studies suggest that imipramine treatment stimulates the release of CPD-containing, SEV-associated DNA. These surprising findings indicate that LEV and SEV generation pathways could be linked in UVB-irradiated cells and that imipramine may exacerbate the systemic effects of extracellular UVR-damaged DNA throughout the body.

Whole blood hydroxychloroquine: Does genetic polymorphism of cytochrome P450 enzymes have a role?

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with a wide range of clinical manifestations and multifactorial etiologies ranging from environmental to genetic. SLE is associated with dysregulated immunological reactions, with increased immune complex formation leading to end-organ damages such as lupus nephritis, cutaneous lupus, and musculoskeletal disorders. Lupus treatment aims to reduce disease activity, prevent organ damage, and improve long-term patient survival and quality of life. Antimalarial, hydroxychloroquine (HCQ) is used as a first-line systemic treatment for lupus. It has shown profound efficacy in lupus and its associated conditions. However, wide variation in terms of clinical response to this drug has been observed among this group of patients. This variability has limited the potential of HCQ to achieve absolute clinical benefits. Several factors, including genetic polymorphisms of cytochrome P450 enzymes, have been stipulated as key entities leading to this inter-individual variation. Thus, there is a need for more studies to understand the role of genetic polymorphisms in CYP450 enzymes in the clinical response to HCQ. Focusing on the role of genetic polymorphism on whole blood HCQ in lupus disorder, this review aims to highlight up-to-date pathophysiology of SLE, the mechanism of action of HCQ, and finally the role of genetic polymorphism of CYP450 enzymes on whole blood HCQ level as well as clinical response in lupus.

DNA-Dependent Interferon Induction and Lung Inflammation in Bordetella pertussis Infection

Pertussis, caused by Bordetella pertussis, is a resurgent respiratory disease but the molecular mechanisms underlying pathogenesis are poorly understood. We recently showed the importance of type I and type III interferon (IFN) induction and signaling for the development of lung inflammation in B. pertussis-infected mouse models. Classically, these IFNs are induced by signaling through a variety of pattern recognition receptors (PRRs) on host cells. Here, we found that the PRR signaling adaptor molecules MyD88 and TRIF contribute to IFN induction and lung inflammatory pathology during B. pertussis infection. However, the PRRs Toll-like receptors (TLR) 3 and TLR4, which signal through TRIF and MyD88, respectively, played no role in IFN induction. Instead, the DNA-sensing PRRs, TLR9 and STING, were important for induction of type I/III IFN and promotion of inflammatory pathology, indicating that DNA is a major inducer of lung IFN responses in B. pertussis infection. These results increase our understanding of this host-pathogen interaction and identify potential targets for host-directed therapies to reduce B. pertussis-mediated pathology.

Significant improvement of systemic lupus erythematosus manifestation in children after autologous dendritic cell transfer: a case report and review of literature

Dendritic cells (DC) are postulated to play a role in autoimmune diseases such as Systemic Lupus Erythematosus (SLE). We reported a 13-year-old female SLE patient who presents with chronic arthritis accompanied by persistent fever, dyspnea, sleep disturbance, headache, stomatitis, rash, and muscle weakness. The supporting examinations showed abnormal blood cell counts, positive antinuclear antibody profile, serositis, and neuropathy. Immunosuppressants failed to improve the condition. DC-based vaccine derived from autologous peripheral blood which was introduced with SARS-CoV-2 protein was given to this patient. There was a significant improvement in clinical and laboratory findings. Thus, DC immunotherapy appears to be a potential novel therapy for SLE that needs to be studied.

Activation of the cGAS-STING innate immune response in cells with deficient mitochondrial topoisomerase TOP1MT

The recognition that cytosolic mitochondrial DNA (mtDNA) activates cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) innate immune signaling has unlocked novel disease mechanisms. Here, an uncharacterized variant predicted to affect TOP1MT function, P193L, was discovered in a family with multiple early onset autoimmune diseases, including Systemic Lupus Erythematosus (SLE). Although there was no previous genetic association between TOP1MT and autoimmune disease, the role of TOP1MT as a regulator of mtDNA led us to investigate whether TOP1MT could mediate the release of mtDNA to the cytosol, where it could then activate the cGAS-STING innate immune pathway known to be activated in SLE and other autoimmune diseases. Through analysis of cells with reduced TOP1MT expression, we show that loss of TOP1MT results in release of mtDNA to the cytosol, which activates the cGAS-STING pathway. We also characterized the P193L variant for its ability to rescue several TOP1MT functions when expressed in TOP1MT knockout cells. We show that the P193L variant is not fully functional, as its re-expression at high levels was unable to rescue mitochondrial respiration deficits, and only showed partial rescue for other functions, including repletion of mtDNA replication following depletion, nucleoid size, steady state mtDNA transcripts levels and mitochondrial morphology. Additionally, expression of P193L at endogenous levels was unable to rescue mtDNA release-mediated cGAS-STING signaling. Overall, we report a link between TOP1MT and mtDNA release leading to cGAS-STING activation. Moreover, we show that the P193L variant has partial loss of function that may contribute to autoimmune disease susceptibility via cGAS-STING mediated activation of the innate immune system.

Pathogenic cellular and molecular mediators in lupus nephritis

Kidney involvement in patients with systemic lupus erythematosus - lupus nephritis (LN) - is one of the most important and common clinical manifestations of this disease and occurs in 40-60% of patients. Current treatment regimens achieve a complete kidney response in only a minority of affected individuals, and 10-15% of patients with LN develop kidney failure, with its attendant morbidity and considerable prognostic implications. Moreover, the medications most often used to treat LN - corticosteroids in combination with immunosuppressive or cytotoxic drugs - are associated with substantial side effects. Advances in proteomics, flow cytometry and RNA sequencing have led to important new insights into immune cells, molecules and mechanistic pathways that are instrumental in the pathogenesis of LN. These insights, together with a renewed focus on the study of human LN kidney tissue, suggest new therapeutic targets that are already being tested in lupus animal models and early-phase clinical trials and, as such, are hoped to eventually lead to meaningful improvements in the care of patients with systemic lupus erythematosus-associated kidney disease.

The cGAS-STING pathway: Post-translational modifications and functional implications in diseases

Recent studies have illustrated the functional significance of DNA recognition in the activation of innate immune responses among a variety of diseases. The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway has been found to be modulated by post-translational modifications and can regulate the immune response via type I IFNs. Accumulating evidence indicates a pivotal role of cGAS-STING signaling, being protective or pathogenic, in the development of diseases. Thus, a comprehensive understanding of the post-translational modifications of cGAS-STING pathway and their role in disease development will provide insights in predicting individual disease outcomes and developing appropriate therapies. In this review, we will discuss the regulation of the cGAS-STING pathway and its implications in disease pathologies, as well as pharmacologic strategies to target the cGAS-STING pathway for therapeutic intervention.

Autoantibodies - enemies, and/or potential allies?

Autoantibodies are well known as potentially highly harmful antibodies which attack the host via binding to self-antigens, thus causing severe associated diseases and symptoms (e.g. autoimmune diseases). However, detection of autoantibodies to a range of disease-associated antigens has enabled their successful usage as important tools in disease diagnosis, prognosis and treatment. There are several advantages of using such autoantibodies. These include the capacity to measure their presence very early in disease development, their stability, which is often much better than their related antigen, and the capacity to use an array of such autoantibodies for enhanced diagnostics and to better predict prognosis. They may also possess capacity for utilization in therapy, in vivo. In this review both the positive and negative aspects of autoantibodies are critically assessed, including their role in autoimmune diseases, cancers and the global pandemic caused by COVID-19. Important issues related to their detection are also highlighted.

Expanding role of deoxyribonucleic acid-sensing mechanism in the development of lifestyle-related diseases

In lifestyle-related diseases, such as cardiovascular, metabolic, respiratory, and kidney diseases, chronic inflammation plays a causal role in their pathogenesis; however, underlying mechanisms of sterile chronic inflammation are not well-understood. Previous studies have confirmed the damage of cells in these organs in the presence of various risk factors such as diabetes, dyslipidemia, and cigarette smoking, releasing various endogenous ligands for pattern recognition receptors. These studies suggested that nucleic acids released from damaged tissues accumulate in these tissues, acting as an endogenous ligand. Undamaged DNA is an integral factor for the sustenance of life, whereas, DNA fragments, especially those from pathogens, are potent activators of the inflammatory response. Recent studies have indicated that inflammatory responses such as the production of type I interferon (IFN) induced by DNA-sensing mechanisms which contributes to self-defense system in innate immunity participates in the progression of inflammatory diseases by the recognition of nucleic acids derived from the host, including mitochondrial DNA (mtDNA). The body possesses several types of DNA sensors. Toll-like receptor 9 (TLR9) recognizes DNA fragments in the endosomes. In addition, the binding of DNA fragments in the cytosol activates cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthase (cGAS), resulting in the synthesis of the second messenger cyclic GMP-AMP (cGAMP). The binding of cGAMP to stimulator of interferon genes (STING) activates NF-κB and TBK-1 signaling and consequently the production of many inflammatory cytokines including IFNs. Numerous previous studies have demonstrated the role of DNA sensors in self-defense through the recognition of DNA fragments derived from pathogens. Beyond the canonical role of TLR9 and cGAS-STING, this review describes the role of these DNA-sensing mechanism in the inflammatory responses caused by endogenous DNA fragments, and in the pathogenesis of lifestyle-related diseases.

Nucleic Acid Sensing and Systemic Lupus Erythematosus: The Danger of Self

This Pillars of Immunology article is a commentary on “Chromatin–IgG complexes activate B cells by dual engagement of IgM and Toll-like receptors,” a pivotal article written by E. A. Leadbetter, I. R. Rifkin, A. M. Hohlbaum, B. C. Beaudette, M. J. Shlomchik and A. Marshak-Rothstein, and published in Nature in 2002. https://www.nature.com/articles/416603a.

Dynamics of DNA damage response markers, RAD51 and XRCC1, throughout the menstrual cycle and pregnancy in healthy women. Increment during pregnancy and relation to a low titer of antinuclear antibodies

PROBLEM

Antinuclear antibodies (ANA) potentially play a role in the pathogenesis of connective tissue diseases (CTDs); however, they are also detected in healthy individuals. Our understanding of the physiological and pathological origin of ANA is incomplete. Both; female reproductive processes and deficiencies in DNA damage response (DDR) have been independently associated with ANA production. However, the link between these two factors and the presence of ANA is unclear METHOD OF STUDY: A cohort study was conducted on 87 non-pregnant and 51 healthy pregnant women. ANA and the DDR markers X-ray repair cross-complementing 1 (XRCC1) and recombinase (RAD51) were quantified in sera by enzyme-linked immunosorbent assay. Additionally, ANA was detected by indirect immunofluorescence in HEp-2 cells in 1:40 diluted sera during the three phases of the menstrual cycle in non-pregnant women and every trimester in pregnant women RESULTS: The prevalence of ANA+ in healthy women was 26.1%, with no significant differences between pregnant and non-pregnant women. ANA and DDR marker levels did not vary among the three phases of the menstrual cycle or the three trimesters of pregnancy. However, DDR marker levels were higher in pregnant women than in non-pregnant women (p<0.001) and were found to be higher in ANA+ women (XRCC1, p = 0.025; RAD51, p = 0.006) CONCLUSIONS: The menstrual cycle and pregnancy did not influence the levels of DDR markers or ANA in healthy women; however, the DDR was higher in pregnancy and ANA+ women. The results suggest a potential role of DDR in the pathophysiology of ANA. This article is protected by copyright. All rights reserved.

The Blood of the HIV-Infected Patients Contains κ-IgG, λ-IgG, and Bispecific κλ-IgG, Which Possess DNase and Amylolytic Activity

Though hundreds of thousands of papers are currently being published on HIV/AIDS, only tens of hundreds of them are devoted to the antibodies generated during the disease. Most of these papers discuss antibodies in HIV/AIDS as a diagnostic tool, and some articles describe neutralizing antibodies as a promising treatment. In this paper, we used affinity chromatography and ELISA to isolate natural IgG from the blood of 26 HIV-infected patients. IgG preparations were separated into the subfractions containing different types of light chains, and catalytic activities of subfractions were analyzed. Here, we show for the first time that the blood of HIV patients contains ~20% of bispecific κλ-IgG, presented with all IgG subclasses. Analysis of DNA-hydrolyzing and amylolytic activity show that most IgG preparations and subfractions are catalytically active. Our results expand the possible biological functions of natural IgG in HIV infection.

Contribution of monocytes and macrophages to the pathogenesis of systemic sclerosis: recent insights and therapeutic implications

PURPOSE OF REVIEW

To discuss recent studies addressing the role of monocytes and macrophages in the pathogenesis of systemic sclerosis (SSc) based on human and mouse models.

RECENT FINDINGS

Studies indicate that monocyte adhesion could be increased in SSc secondary to an interferon-dependent loss of CD52, and chemotaxis up-regulated through the CCR3/CCL24 pathway. Beyond the conventional M1/M2 paradigm of macrophage subpopulations, new subpopulations of macrophages have been recently described in skin and lung biopsies from SSc patients. Notably, single-cell ribonucleic acid sequencing has provided evidence for SPP1+ lung macrophages or FCGR3A+ skin macrophages in SSc. Impaired pro-resolving capacities of macrophages such as efferocytosis, i.e. the ability to phagocyte apoptotic cells, could also participate in the inflammatory and autoimmune features in SSc.

SUMMARY

Through their potential pro-fibrotic and pro-inflammatory properties, macrophages are at the cross-road of key SSc pathogenic processes and associated manifestations. Investigative drugs targeting macrophage polarization, such as pan-janus kinase inhibitors (tofacitinib or ruxolitinib) impacting both M1 and M2 activations, or Romilkimab inhibiting IL-4 and IL-13, have shown promising results in preclinical models or phase I/II clinical trials in SSc and other fibro-inflammatory disorders. Macrophage-based cellular therapy may also represent an innovative approach for the treatment of SSc, as initial training of macrophages may modulate the severity of fibrotic and autoimmune manifestations of the disease.

Plasma microparticles from patients with systemic lupus erythematosus modulate the content of miRNAs in U937 cells

In systemic lupus erythematosus (SLE), the clearance of apoptotic cells and microparticles (MPs) is reduced. Some MPs contain molecules that can modulate immune responses. This study aimed to evaluate the presence of miR-126 and miR-146a in plasma MPs of patients with SLE (SLE MPs) and analyse the ability of MPs to modulate some events in the promonocytic U937 cell line. Circulating MPs were isolated from plasma samples of healthy controls (HCs), patients with SLE and other autoimmune diseases (OAD). MPs were analysed for size and cell origin by flow cytometry and content of miR-126 and miR-146a by RT-qPCR. MPs were then added to U937 cell cultures to evaluate changes in cell phenotype, cytokine expression, content of miR-126 and miR-146a, and levels of IRF5. Patients with active SLE (aSLE) showed an increase in concentration of plasma MPs that positively correlated with the SLEDAI (SLE Disease Activity Index) score. CD14+ MPs were significantly more abundant in patients with SLE than HCs. SLE MPs contained decreased levels of miR-146a, but the miR-126 content in aSLE MPs was increased. The miR-126 content in SLE MPs correlated positively with the SLEDAI score. The treatment of U937 cells with MPs from HCs and patients induced reduced expression of HLA-DR, CD18 and CD119, increased frequency of IL-6+ and TNF-α+ cells, accumulation of IL-8 in culture supernatants, increased miR-126 levels and decreased miR-146a content, but no change in the expression of IRF5. These findings suggest that plasma MPs, especially SLE MPs, could modulate some biological events in U937 cells.

Emerging Roles of the Innate Immune System Regulated by DNA Sensors in the Development of Vascular and Metabolic Diseases

Sterile chronic inflammation causes cardiometabolic disorders; however, the mechanisms are not fully understood. Previous studies have demonstrated the degradation of cells/tissues in the vasculature and metabolic organs in lifestyle-associated diseases, such as diabetes and hyperlipidemia, suggesting the release and/or accumulation of nucleic acids from damaged cells. DNA is indispensable for life; however, DNA fragments, especially those from pathogens, strongly induce inflammation by the activation of DNA sensors. Growing evidence suggests that DNA-sensing mechanisms, which are normally involved in self-defense against pathogens as the innate immune system, are associated with the progression of inflammatory diseases in response to endogenous DNA fragments. There are several types of DNA sensors in our bodies. Toll-like receptor 9 (TLR9)—one of the most studied DNA sensors—recognizes DNA fragments in endosome. In addition, stimulator of interferon genes (STING), which has recently been extensively investigated, recognizes cyclic GMP-AMP (cGAMP) generated from DNA fragments in the cytosol. Both TLR9 and STING are known to play pivotal roles in host defense as the innate immune system. However, recent studies have indicated that the activation of these DNA sensors in immune cells, such as macrophages, promotes inflammation leading to the development of vascular and metabolic diseases associated with lifestyle. In this review, we discuss recent advances in determining the roles of DNA sensors in these disease contexts. Revealing a novel mechanism of sterile chronic inflammation regulated by DNA sensors might facilitate clinical interventions for these health conditions.

Systemic Lupus Erythematosus Disease: An Overview of the Clinical Approach to Pathogenesis, Diagnosis, and Treatment

The systemic lupus erythematosus (SLE), commonly known as Lupus, is a rare and complex multisystem autoimmune disease where one’s immune system is overactive, and the body attacks its organ systems. SLE is a historically old disease described already in antiquity; it is an example of a chronic disease with physical, psychological, financial, and social implications for individuals diagnosed. It has inspired medical and basic biological scientists that focus on molecular biology, basic immunology, immunopathology, clinical science, genetics, and epidemiology. The syndrome is real in its existence-although hidden behind obstacles, cumbersome for patients and clinicians, and rebellious for scientists. There is currently no cure for SLE. The goal of treatment is to ease symptoms. This article will review information on the general approach to SLE therapy, focusing on currently approved therapies and novel approaches that might be used in the future.

Sustained high expression of multiple APOBEC3 cytidine deaminases in systemic lupus erythematosus

APOBEC3 (A3) enzymes are best known for their role as antiviral restriction factors and as mutagens in cancer. Although four of them, A3A, A3B, A3F and A3G, are induced by type-1-interferon (IFN-I), their role in inflammatory conditions is unknown. We thus investigated the expression of A3, and particularly A3A and A3B because of their ability to edit cellular DNA, in Systemic Lupus Erythematosus (SLE), a chronic inflammatory disease characterized by high IFN-α serum levels. In a cohort of 57 SLE patients, A3A and A3B, but also A3C and A3G, were upregulated ~ 10 to 15-fold (> 1000-fold for A3B) compared to healthy controls, particularly in patients with flares and elevated serum IFN-α levels. Hydroxychloroquine, corticosteroids and immunosuppressive treatment did not reverse A3 levels. The A3AΔ3B polymorphism, which potentiates A3A, was detected in 14.9% of patients and in 10% of controls, and was associated with higher A3A mRNA expression. A3A and A3B mRNA levels, but not A3C or A3G, were correlated positively with dsDNA breaks and negatively with lymphopenia. Exposure of SLE PBMCs to IFN-α in culture induced massive and sustained A3A levels by 4 h and led to massive cell death. Furthermore, the rs2853669 A > G polymorphism in the telomerase reverse transcriptase (TERT) promoter, which disrupts an Ets-TCF-binding site and influences certain cancers, was highly prevalent in SLE patients, possibly contributing to lymphopenia. Taken together, these findings suggest that high baseline A3A and A3B levels may contribute to cell frailty, lymphopenia and to the generation of neoantigens in SLE patients. Targeting A3 expression could be a strategy to reverse cell death and the generation of neoantigens.

Lupus Membranous Nephropathy

Background

Lupus membranous nephropathy (LMN) is a rare disease, usually associated with nephrotic syndrome.

Methods

We reviewed the literature by searching for the following terms on Pubmed.gov: lupus nephritis, membranous nephropathy (MN), lupus membranous nephropathy, nephrotic syndrome, and Class V lupus nephritis.

Results

The histology of LMN at light microscopy is similar to that of primary MN. Cases of MN associated with focal or diffuse proliferation are not considered LMN by the International Society of Nephrology/Renal Pathology Society classification. Immunofluorescence study of LMN shows deposits of all immunoglobulins and complement. Tubulo-reticular structures, extraglomerular deposits, subepithelial, and scanty subendothelial deposits can be seen on electron microscopy. Phospholipase A2 receptor deposits are usually but not necessarily absent in LMN. The pathogenesis is still not completely understood. The inflammatory milieu of lupus may favor the development of autoantigens and intraglomerular assembly of immune complexes. These are more often associated with mesangial or endocapillary hypercellular lesions. Alternatively, autoantibodies may bind autoantigens in the glomerular subepithelium, triggering a signaling cascade leading to LMN. A central role in the development of podocyte injury and proteinuria is played by the components of complement C5b-C9. CKD progression in LMN is slow but may be accelerated by the frequency of renal flares. Persistent nephrotic syndrome and/or the frequent use of corticosteroids may lead to a series of life-threatening complications.

Discussion

Treatment of arterial hypertension, dyslipidemia, and diabetes are of paramount importance. Besides specific therapies of these complications, hydroxychloroquine and vitamin D supplementation are recommended. Immunosuppression should be limited to patients with nephrotic proteinuria. The most frequently used drugs are corticosteroids, calcineurin inhibitors, cyclophosphamide, mycophenolate, and rituximab, alone or combined. Early detection and treatment of renal flares is of paramount importance to prevent CKD progression.

Complementary Effects of Carbamylated and Citrullinated LL37 in Autoimmunity and Inflammation in Systemic Lupus Erythematosus

LL37 acts as T-cell/B-cell autoantigen in Systemic lupus erythematosus (SLE) and psoriatic disease. Moreover, when bound to "self" nucleic acids, LL37 acts as "danger signal," leading to type I interferon (IFN-I)/pro-inflammatory factors production. T-cell epitopes derived from citrullinated-LL37 act as better antigens than unmodified LL37 epitopes in SLE, at least in selected HLA-backgrounds, included the SLE-associated HLA-DRB1*1501/HLA-DRB5*0101 backgrounds. Remarkably, while "fully-citrullinated" LL37 acts as better T-cell-stimulator, it loses DNA-binding ability and the associated "adjuvant-like" properties. Since LL37 undergoes a further irreversible post-translational modification, carbamylation and antibodies to carbamylated self-proteins other than LL37 are present in SLE, here we addressed the involvement of carbamylated-LL37 in autoimmunity and inflammation in SLE. We detected carbamylated-LL37 in SLE-affected tissues. Most importantly, carbamylated-LL37-specific antibodies and CD4 T-cells circulate in SLE and both correlate with disease activity. In contrast to "fully citrullinated-LL37," "fully carbamylated-LL37" maintains both innate and adaptive immune-cells' stimulatory abilities: in complex with DNA, carbamylated-LL37 stimulates plasmacytoid dendritic cell IFN-α production and B-cell maturation into plasma cells. Thus, we report a further example of how different post-translational modifications of a self-antigen exert complementary effects that sustain autoimmunity and inflammation, respectively. These data also show that T/B-cell responses to carbamylated-LL37 represent novel SLE disease biomarkers.

Mir-331-3p Inhibits PRRSV-2 Replication and Lung Injury by Targeting PRRSV-2 ORF1b and Porcine TNF-α

Porcine reproductive and respiratory syndrome (PRRS) caused by a single-stranded RNA virus (PRRSV) is a highly infectious respiratory disease and leads to huge economic losses to the swine industry worldwide. To investigate the role of miRNAs in the infection and lung injury induced by PRRSV, the differentially expressed miRNAs (DE-miRs) were isolated from PRRSV-2 infected/mock-infected PAMs of Meishan, Landrace, Pietrain, and Qingping pigs at 9, 36, and 60 hpi. Mir-331-3p was the only common DE-miR in each set of miRNA expression profile at 36 hpi. Mir-210 was one of 7 common DE-miRs between PRRSV infected and mock-infected PAMs of Meishan, Pietrain, and Qingping pigs at 60 hpi. Mir-331-3p/mir-210 could target PRRSV-2 ORF1b, bind and downregulate porcine TNF-α/STAT1 expression, and inhibit PRRSV-2 replication, respectively. Furthermore, STAT1 and TNF-α could mediate the transcriptional activation of MCP-1, VCAM-1, and ICAM-1. STAT1 could also upregulate the expression of TNF-α by binding to its promoter region. In vivo, pEGFP-N1-mir-331-3p could significantly reduce viral replication and pathological changes in PRRSV-2 infected piglets. Taken together, Mir-331-3p/mir-210 have significant roles in the infection and lung injury caused by PRRSV-2, and they may be promising therapeutic targets for PRRS and lung injury/inflammation.

Emerging roles of Toll-like receptor 9 in cardiometabolic disorders

Growing evidence suggests that damage-associated molecule patterns (DAMPs) and their receptors, pattern recognition receptors (PRRs), are associated with the progression of cardiometabolic disorders, including obesity-related insulin resistance and atherosclerosis. Cardiometabolic disorders share sterile chronic inflammation as a major cause; however, the exact mechanisms are still obscure. Toll-like receptor 9 (TLR9), one of the nucleic acid-sensing TLRs, recognizes DNA fragments derived from pathogens and contributes to self-defense by activation of the innate immune system. In addition, previous studies demonstrated that TLR9 recognizes DNA fragments released from host cells, accelerating sterile inflammation, which is associated with inflammatory diseases such as autoimmune diseases. In obese adipose tissue and atherosclerotic vascular tissue, various stresses release DNA fragments and/or nuclear proteins as DAMPs from degenerated adipocytes and vascular cells. Recent studies indicated that the activation of TLR9 in immune cells including macrophages and dendritic cells by recognition of these DAMPs promotes inflammation in these tissues, which causes cardiometabolic disorders. This review discusses recent advances in understanding the role of sterile inflammation associated with TLR9 and its endogenous ligands in cardiometabolic disorders. New insights into innate immunity may provide better understanding of cardiometabolic disorders and new therapeutic options for these major health threats in recent decades.

The hallmarks of severe pulmonary arterial hypertension: the cancer hypothesis-ten years later

Severe forms of pulmonary arterial hypertension (PAH) are most frequently the consequence of a lumen-obliterating angiopathy. One pathobiological model is that the initial pulmonary vascular endothelial cell injury and apoptosis is followed by the evolution of phenotypically altered, apoptosis-resistant, proliferating cells and an inflammatory vascular immune response. Although there may be a vasoconstrictive disease component, the increased pulmonary vascular shear stress in established PAH is caused largely by the vascular wall pathology. In this review, we revisit the "quasi-malignancy concept" of severe PAH and examine to what extent the hallmarks of PAH can be compared with the hallmarks of cancer. The cancer model of severe PAH, based on the growth of abnormal vascular and bone marrow-derived cells, may enable the emergence of novel cell-based PAH treatment strategies.

Base Excision Repair in the Immune System: Small DNA Lesions With Big Consequences

The integrity of the genome is under constant threat of environmental and endogenous agents that cause DNA damage. Endogenous damage is particularly pervasive, occurring at an estimated rate of 10,000–30,000 per cell/per day, and mostly involves chemical DNA base lesions caused by oxidation, depurination, alkylation, and deamination. The base excision repair (BER) pathway is primary responsible for removing and repairing these small base lesions that would otherwise lead to mutations or DNA breaks during replication. Next to preventing DNA mutations and damage, the BER pathway is also involved in mutagenic processes in B cells during immunoglobulin (Ig) class switch recombination (CSR) and somatic hypermutation (SHM), which are instigated by uracil (U) lesions derived from activation-induced cytidine deaminase (AID) activity. BER is required for the processing of AID-induced lesions into DNA double strand breaks (DSB) that are required for CSR, and is of pivotal importance for determining the mutagenic outcome of uracil lesions during SHM. Although uracils are generally efficiently repaired by error-free BER, this process is surprisingly error-prone at the Ig loci in proliferating B cells. Breakdown of this high-fidelity process outside of the Ig loci has been linked to mutations observed in B-cell tumors and DNA breaks and chromosomal translocations in activated B cells. Next to its role in preventing cancer, BER has also been implicated in immune tolerance. Several defects in BER components have been associated with autoimmune diseases, and animal models have shown that BER defects can cause autoimmunity in a B-cell intrinsic and extrinsic fashion. In this review we discuss the contribution of BER to genomic integrity in the context of immune receptor diversification, cancer and autoimmune diseases.

In vivo evidence for extracellular DNA trap formation

Extracellular DNA trap formation is a cellular function of neutrophils, eosinophils, and basophils that facilitates the immobilization and killing of invading microorganisms in the extracellular milieu. To form extracellular traps, granulocytes release a scaffold consisting of mitochondrial DNA in association with granule proteins. As we understand more about the molecular mechanism for the formation of extracellular DNA traps, the in vivo function of this phenomenon under pathological conditions remains an enigma. In this article, we critically review the literature to summarize the evidence for extracellular DNA trap formation under in vivo conditions. Extracellular DNA traps have not only been detected in infectious diseases but also in chronic inflammatory diseases, as well as in cancer. While on the one hand, extracellular DNA traps clearly exhibit an important function in host defense, it appears that they can also contribute to the maintenance of inflammation and metastasis, suggesting that they may represent an interesting drug target for such pathological conditions.

Metabolic Targets for Treatment of Autoimmune Diseases

There is a considerable unmet demand for safe and efficacious medications in the realm of autoimmune and inflammatory diseases. The fate of the immune cells is precisely governed by control of various metabolic processes such as mitochondrial oxidative phosphorylation, glycolysis, fatty acid synthesis, beta-oxidation, amino acid metabolism, and several others including the pentose phosphate pathway, which is a unique source of metabolites for cell proliferation and maintenance of a reducing environment. These pathways are tightly regulated by the cytokines, growth factors, availability of the nutrients and host-microbe interaction. Exploring the immunometabolic pathways that govern the fate of cells of the innate and adaptive immune system, during various stages of activation, proliferation, differentiation and effector response, is crucial for new development of new treatment targets. Identifying the pathway connections and key enzymes will help us to target the dysregulated inflammation in autoimmune diseases. The mechanistic target of rapamycin (mTOR) pathway is increasingly recognized as one of the key drivers of proinflammatory responses in autoimmune diseases. In this review, we provide an update on the current understanding of the metabolic signatures noted within different immune cells of many different autoimmune diseases with a focus on selecting pathways and specific metabolites as targets for treatment.